Several members of the protein kinase family have been clearly implicated in the pathogenesis of various proliferative and myeloproliferative diseases and thus represent important targets for treatment of these diseases. Some of the proliferative diseases relevant to this invention include cancer, rheumatoid arthritis, atherosclerosis, and retinopathies. Important examples of kinases which have been shown to cause or contribute to the pathogenesis of these diseases include C-Abl kinase and the oncogenic fusion protein bcr-Abl kinase; c-Kit kinase, c-MET, the HER family, PDGF receptor kinase, VEGF receptor kinases, Flt-3 kinase and the Raf kinase family.
C-Abl kinase is an important non-receptor tyrosine kinase involved in cell signal transduction. This ubiquitously expressed kinase—upon activation by upstream signaling factors including growth factors, oxidative stress, integrin stimulation, and ionizing radiation—localizes to the cell plasma membrane, the cell nucleus, and other cellular compartments including the actin cytoskeleton (Van Etten, Trends Cell Biol. (1999) 9: 179). There are two normal isoforms of Abl kinase: Abl-1A and Abl-1B. The N-terminal half of c-Abl kinase is important for autoinhibition of the kinase domain catalytic activity (Pluk et al, Cell (2002) 108: 247). Details of the mechanistic aspects of this autoinhibition have recently been disclosed (Nagar et al, Cell (2003) 112: 859). The N-terminal myristolyl amino acid residue of Abl-1B has been shown to intramolecularly occupy a hydrophobic pocket formed from alpha-helices in the C-lobe of the kinase domain. Such intramolecular binding induces a novel binding area for intramolecular docking of the SH2 domain and the SH3 domain onto the kinase domain, thereby distorting and inhibiting the catalytic activity of the kinase. Thus, an intricate intramolecular negative regulation of the kinase activity is brought about by these N-terminal regions of c-Abl kinase. An aberrant dysregulated form of c-Abl is formed from a chromosomal translocation event, referred to as the Philadelphia chromosome (P. C. Nowell et al, Science (1960) 132: 1497; J. D. Rowley, Nature (1973) 243: 290). This abnormal chromosomal translocation leads aberrant gene fusion between the Abl kinase gene and the breakpoint cluster region (BCR) gene, thus encoding an aberrant protein called bcr-Abl (G. Q. Daley et al, Science (1990) 247: 824; M. L. Gishizky et al, Proc. Natl. Acad. Sci. USA (1993) 90: 3755; S. Li et al, J. Exp. Med. (1999) 189: 1399). The bcr-Abl fusion protein does not include the regulatory myristolyation site (B. Nagar et al, Cell (2003) 112: 859) and as a result functions as an oncoprotein which causes chronic myeloid leukemia (CML). CML is a malignancy of pluripotent hematopoietic stem cells. The p210 form of bcr-Abl is seen in 95% of patients with CML, and in 20% of patients with acute lymphocytic leukemia. A p185 form has also been disclosed and has been linked to being causative of up to 10% of patients with acute lymphocytic leukemia.
The majority of small molecule kinase inhibitors that have been reported have been shown to bind in one of three ways. Most of the reported inhibitors interact with the ATP binding domain of the active site and exert their effects by competing with ATP for occupancy. Other inhibitors have been shown to bind to a separate hydrophobic region of the protein known as the “DFG-in-conformation” pocket, and still others have been shown to bind to both the ATP domain and the “DFG-in-conformation” pocket. Examples specific to inhibitors of Raf kinases can be found in Lowinger et al, Current Pharmaceutical Design (2002) 8: 2269-2278; Dumas, J. et al., Current Opinion in Drug Discovery & Development (2004) 7: 600-616; Dumas, J. et al, WO 2003068223 A1 (2003); Dumas, J., et al, WO 9932455 A1 (1999), and Wan, P. T. C., et al, Cell (2004) 116: 855-867.
Physiologically, kinases are regulated by a common activation/deactivation mechanism wherein a specific activation loop sequence of the kinase protein binds into a specific pocket on the same protein which is referred to as the switch control pocket (see WO 200380110049 for further details). Such binding occurs when specific amino acid residues of the activation loop are modified for example by phosphorylation, oxidation, or nitrosylation. The binding of the activation loop into the switch pocket results in a conformational change of the protein into its active form (Huse, M. and Kuriyan, J. Cell (109) 275-282).